The Lockheed B-37 was intended to be an armed reconnaissance/observation derivative of the Lockheed Lodestar. Initially designated O-56, the aircraft was later redesignated RB-34B, and finally B-37 because a different engine would be used on the B-37 (Wright R-2600 rather than the Pratt & Whitney R-2800 used on the B-34).

The U.S. Army Air Corps placed an order for 550 aircraft on Aug. 8, 1941, five days before the initial B-34 order. Only 18 B-37s were actually completed before the entire order was canceled to allow Lockheed to shift production to higher priority projects. The first flight of a B-37 was on Sept. 21, 1942.